1. Field of the Invention
The present invention is directed to a zoom lens and an image pickup apparatus having the zoom lens, and more particularly, to a zoom lens which is suitable for a digital camera, a video camera, a silver-halide film camera, and the like.
2. Description of the Related Art
Recently, a zoom lens having a wide angle of view, a high zoom ratio, and a small size has been in demand for a photographic optical system used for an image pickup apparatus such as a video camera or a digital still camera using a solid-state image sensor. As a method of miniaturizing an image pickup apparatus, there is known a retractable lens barrel, which allows an axial length of a zoom lens in an optical axis direction to be small during a non-photographing state by changing a distance between respective lens units of the zoom lens in a photographing state to become smaller. As a zoom lens that allows an easy reduction in size of the entire zoom lens and easy widening of an angle of view, there is known a negative lead type zoom lens, in which a lens unit having a negative refractive power is closest to an object side.
For example, there is known a three-unit zoom lens which includes, in order from an object side to an image side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a positive refractive power to perform zooming by moving the lens units.
U.S. Pat. No. 7,453,648 discusses a three-unit zoom lens having a zoom ratio of about three and a half angle of view of about 35 degrees at an wide-angle end, in which a material having a high refractive index and high-dispersion is used for a positive lens in a first lens unit.
Besides, as a negative lead type zoom lens, there is known a two-unit zoom lens which includes, in order from an object side to an image side, a first lens unit having a negative refractive power and a second lens unit having a positive refractive power to perform zooming by moving the lens units.
U.S. Patent Application Publication No. 2010/0245629 discusses a two-unit zoom lens having a zoom ratio of about three and a half angle of view of about 32 degrees at an wide-angle end, in which a material having a high refractive index and high-dispersion is used for a positive lens in a first lens unit.
As a method of miniaturizing a zoom lens, it is very effective to use a retractable lens barrel. However, when an amount of movement of each lens unit during zooming and focusing is large, the total lens length increases. As a result, although the retractable lens barrel is used, since a retraction length which is a length when the lens is retracted is large, it is difficult to miniaturize an image pickup apparatus.
In a negative lead type zoom lens, in shortening the retraction length, it is important to make the thickness of each lens unit as small as possible and preventing an effective diameter of the front lens from increasing. In addition, to correct chromatic aberration of magnification and curvature of field over entire zoom range and to miniaturize an entire zoom lens, it is important to appropriately set a refractive power arrangement of the first lens unit and a lens configuration of each lens unit.
In the zoom lens discussed in U.S. Pat. No. 7,453,648, the first lens unit includes one negative lens and one positive lens. In addition, the positive lens in the first lens unit is configured by using a material having a high refractive index, so that the thickness of the first lens unit decreases. However, since a physical stop is disposed at an object side of the second lens unit, the thickness in the optical axis direction during retraction tends to be increased.
In addition, at a telephoto end, it is difficult to reduce a distance between an image-side principal position of the first lens unit and an object-side principal position of the second lens unit to the utmost limits thereof. For this reason, it is difficult to decrease the thickness of each lens unit by weakening the refractive power of the second lens unit. In addition, since the refractive power of the first lens unit is small, when an aperture stop is considered to be disposed at an object side of the second lens unit, the effective diameter of the front lens is increased.
On the other hand, in the zoom lens discussed in U.S. Patent Application Publication No. 2010/0245629, the first lens unit includes one negative lens, an air distance, and one positive lens. In addition, a small thickness of the first lens unit is implemented by configuring the positive lens in the first lens unit by using a material having a high refractive index. In addition, a small thickness in the optical axis direction during retraction is implemented by configuring the second lens unit with no physical stop. However, since the distance between the first lens unit and the second lens unit at a telephoto end is large, the size of the entire zoom lens tends to be increased.
In general, in a negative lead type two-unit or three-unit zoom lens, to decrease the thickness of the entire zoom lens during retraction and obtain a high optical performance, it is important to make an appropriate lens configuration of a first lens unit having a negative refractive power. When the lens configuration of the first lens unit is not appropriate, it is difficult to miniaturize the entire zoom lens and obtain a high optical performance over the entire zoom range with a high zoom ratio.